1. Field of the Invention
This invention relates to a liquid crystal display comprising an electrostatic protection circuit and a test circuit.
2. Description of the Related Art
In conventional active matrix type liquid crystal displays, there is a need to prevent faults such as a characteristic shift and dielectric breakdown of a switching thin film transistor due to static electricity. Jpn. Pat. Appln. KOKAI Publication No. 2005-93459 has disclosed a liquid crystal display having an electrostatic protection circuit for preventing such faults. This electrostatic protection circuit is provided outside a display region where there are provided pixel electrodes in the vicinity of intersections between a plurality of scan lines and a plurality of data lines that are provided in matrix form and switching thin film transistors connected to the pixel electrodes. This electrostatic protection circuit comprises a plurality of scan line electrostatic protection lines, a scan line electrostatic protection thin film transistor provided between each scan line electrostatic protection line and each scan line, a plurality of data line electrostatic protection lines, and a data line electrostatic protection thin film transistor provided between each data line electrostatic protection line and each data line.
In the above-mentioned conventional liquid crystal display, the scan line electrostatic protection lines and the scan line electrostatic protection thin film transistors, and the data line electrostatic protection lines and the data line electrostatic protection thin films are provided outside the display region, and securing regions to arrange these components leads to a problem of an increased frame size. Here, the frame size means the size of a non-display region in a display panel of the liquid crystal display, and this size is called the frame size because a region except for the display region in the display panel of the liquid crystal display is shaped into a frame for housing a picture.
Furthermore, when such a conventional liquid crystal display is inspected for, for example, a line defect, a test terminal may be provided outside the display region on the opposite sides of the regions where the scan line electrostatic protection thin film transistors and the data line electrostatic protection thin film transistors are provided. In that case, in order to selectively drive the scan lines and the data lines, a scan line test thin film transistor and a data line test thin film transistor have to be arranged between the test terminal and each scan line and each data line, and securing regions to arrange these components leads to a problem of a further increased frame area.